Hi Rich, On Monday, 9 April 2018 18:11:13 EEST Rich Felker wrote: > On Mon, Apr 09, 2018 at 04:06:15PM +0300, Laurent Pinchart wrote: > > On Monday, 9 April 2018 14:11:22 EEST Robin Murphy wrote: > >> On 09/04/18 08:25, jacopo mondi wrote: > >>> Hi Robin, Laurent, > >>> > >>> a long time passed, sorry about this. > >>> > >>> On Wed, Nov 15, 2017 at 01:38:23PM +0000, Robin Murphy wrote: > >>>> On 14/11/17 17:08, Jacopo Mondi wrote: > >>>>> On SH4 architecture, with SPARSEMEM memory model, translating page > >>>>> to pfn hangs the CPU. Post-pone translation to pfn after > >>>>> dma_mmap_from_dev_coherent() function call as it succeeds and make > >>>>> page translation not necessary. > >>>>> > >>>>> This patch was suggested by Laurent Pinchart and he's working to > >>>>> submit a proper fix mainline. Not sending for inclusion at the > >>>>> moment. > >>>> > >>>> Y'know, I think this patch does have some merit by itself - until we > >>>> know that cpu_addr *doesn't* represent some device-private memory > >>>> which is not guaranteed to be backed by a struct page, calling > >>>> virt_to_page() on it is arguably semantically incorrect, even if it > >>>> might happen to be benign in most cases. > >>> > >>> I still need to carry this patch in my trees to have a working dma > >>> memory mapping on SH4 platforms. My understanding from your comment is > >>> that there may be a way forward for this patch, do you still think the > >>> same? Have you got any suggestion on how to improve this eventually > >>> for inclusion? > >> > >> As before, the change itself does seem reasonable; it might be worth > >> rewording the commit message in more general terms rather than making it > >> sound like an SH-specific workaround (which I really don't think it is), > >> but otherwise I'd say just repost it as a non-RFC patch. > > > > I actually can't remember any better fix I would have in mind, so this > > looks good to me :-) I agree with Robin, the commit message should be > > reworded. Robin's explanation of why virt_to_page() should be postponed > > until we know that cpu_addr represents memory that is guaranteed to be > > backed by a struct page is a good starting point. You can mention SH4 as > > an example of an architecture that will crash when calling virt_to_page() > > in such a case, but the fix isn't specific to SH4. > > Just checking since I joined late -- is the consensus that this does > not require any action/review specific to SH (in my role as maintainer > way behind on maintenance)? I don't think it requires any action specific to SH. If you want to review the patch in the context of SH though, please feel free to do so :-) -- Regards, Laurent Pinchart
